Breathable packaging film having enhanced thermoformability

ABSTRACT

The present invention describes thermoformable coextruded film suitable for use in packaging applications having at least a first polymeric layer serving as an outermost exterior-film layer and comprising a cycloaliphatic polyester, an aromatic polyester or blends thereof; a second polymeric layer serving as a thermoforming-assist layer and comprising a polyolefin; and a third polymeric layer serving as an innermost exterior-film layer and comprising a heat-sealing polyolefinic material. The films of the present invention are oxygen-permeable in that they exhibit an oxygen transmission rate of between 2-1000 cm 3 /100 in 2 /24 h.atm.

FIELD OF THE INVENTION

The present invention generally relates to food packaging films, andparticularly, to thermoformable coextruded packaging films havingspecial utility in the packaging of fresh poultry, meats, fruits andvegetables.

BACKGROUND OF THE INVENTION

Thermoforming and other similar techniques are well known in the art forpackaging products. Suitable thermoforming methods, for example, includea vacuum forming or plug-assist vacuum forming method. In the vacuumforming method, a first film is heated, for example, by a contact heaterand a vacuum is applied beneath the film causing the web to be pushed byatmospheric pressure down into a preformed mold. In a plug-assist vacuumforming method, after the first or forming film has been heated andsealed across a mold cavity, a plug shape similar to the mold shapeimpinges on the forming film and, upon the application of vacuum, theforming film transfers to the mold surface. After the forming film is inplace, a product is placed, such as by manual loading, on the formingfilm and a second, substantially non-thermoforming film is disposed overthe product. At a sealing station, the packages are evacuated and fusionsealed with a sealing device such as a heated jaw. The first orthermoforming film encloses a substantial portion, generally more thanhalf, of the product to be packaged.

Thermoforming is a popular method of making packaging for food products,particularly, fresh and frozen meats. In the packaging of such products,it is desirable to allow oxygen to permeate a film or package so as tocontact the meat product contained therein. For example, a packageutilizing a permeable film can permit oxygen to permeate to a fresh redmeat in the package, thereby allowing the meat product to oxygenate(often referred to as blooming which causes the meat color to changefrom purple to a consumer desirable red color). This can enhanceconsumer appeal, and retail vendors of such meat products demand thistype of capability. Additionally, many types of produce require thepresence of oxygen to suppress anaerobic spoilage.

Also in packaging of such products, it is desirable to provide a clearpackage to permit observation of the enclosed product with the packaginghaving good optical properties such as clarity and gloss in order toenhance package appearance for the consumer.

Not withstanding the fairly high state of development in the art,packaging manufacturers are continually striving to improve thefunctionality of their packaging materials.

SUMMARY OF THE INVENTION

This present invention relates to thermoformable coextruded packagingfilms which provide oxygen permeability, improved thermoformability andgood optical characteristics. It is a more particular object of thepresent invention to provide a material for packaging food productsrequiring oxygen permeability such as, for example, fresh poultry, freshand frozen red meat and fresh produce. The present invention providessuch films which have an oxygen transmission rate at 73° C. and 0% R.H.of between 2-1000 cm³/100 in²/24 h. (31-15,500 cm³/m²/24 h.) as measuredin accordance with ASTM D-3985-02 test method.

It is another object of the present invention to provide a coextrudedpackaging film having improved thermoformability. The present inventionprovides such thermoformable multilayer films which are particularlywell suited for forming a package in which the film is molded into acavity in which a product may be placed. Such multilayer films may becharacterized as having a linear free shrink at 80° C. of 0-5% in boththe machine and transverse directions as measure in accordance with ASTMD-2732-96 test method.

It is yet another object of the present invention to provide athermoformable coextruded packaging film which exhibits exceptionaloptical properties. The present invention provides multilayer filmshaving a gloss value at 45° of at least 60% as measure in accordancewith ASTM D-2457-03 test method and a haze value of less than 20% asmeasured in accordance with ASTM D-1003-00 test method.

Such objects generally are achieved by a thermoformable coextrudedpackaging film having a multilayer film structure comprising at leastthree polymeric layers which includes a first polymeric layer as anoutermost exterior-film layer comprising homopolymers or copolymers ofpolypropylene an aromatic polyester, a cycloaliphatic polyester orblends thereof, a second polymeric layer as an interior-film,thermoforming-assist layer comprising homopolymers or copolymers ofpolyolefin, preferably, polypropylene or cross-linked polyethylene, anda third polymeric layer as an innermost exterior-film layer comprising aheat-sealing polyolefin.

Such objects more particularly may be achieved by above-described filmstructures which include a first polymeric layer comprising an aromaticester derived from homopolymers and copolymers of alkyl-aromatic esters,such as, for example, polyethylene terephthalate (“PET”), amorphouspolyethylene terephthalate (“APET”), crystalline polyethyleneterephthalate (“CPET”), glycol-modified polyethylene terephthalate(“PETG”), and polybutylene terephthalate; copolymers of isophthalate,such as, polyethylene terephthalate/isophthalate copolymer, orcycloaliphatic esters, and blends of any of the aforementionedmaterials. The films may include layers in addition to those describedabove. For instance, the multilayer films of the present invention mayinclude a film structure comprising a fourth polymeric layer such as atie layer positioned between the first polymeric layer and the secondpolymeric layer. Preferably, the fourth layer includes a materialderived from polyalkyl acrylate copolymers, more preferably,ethylene/alkyl acrylate copolymers, and most preferably, a materialselected from the group consisting of ethylene/methyl acrylate copolymer(“E/MA”), ethylene/ethyl acrylate copolymer (“E/EA”), ethylene/butylacrylate copolymer (“E/BA”), and ethylene/methyl methacrylate copolymer(“E/MMA”).

These and other aspects, advantages, and features of the invention willbe more readily understood and appreciated by reference to the detaileddescription of the invention and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially schematic, cross-sectional view of one embodimentof a multilayer packaging film according to the present inventioncomprising four layers.

FIG. 2 is a partially schematic, cross-sectional view of anotherembodiment of a multilayer film according to the present inventioncomprising seven layers.

DETAILED DESCRIPTION OF THE INVENTION

As used herein, the term “film” is used in the generic to includeplastic web, regardless of whether it is a film or sheet.

As used herein, the phrase “thermoplastic” refers to a polymer orpolymer mixture that softens when exposed to heat and returns to itsoriginal condition when cooled to room temperature. In general,thermoplastic materials include, but are not limited too, syntheticpolymers such as polyesters, polyolefins, polyamides, polystyrenes, andthe like. Thermoplastic materials may also include synthetic polymersthat are cross-linked by either radiation or chemical reaction during amanufacturing or post-manufacturing process operation.

As used herein, the term “polymeric” refers to a material which is theproduct of a polymerization reaction of natural, synthetic, or naturaland synthetic ingredients, and is inclusive of homopolymers, copolymers,terpolymers, etc. In general, the layers of a film or substrate maycomprise a single polymer, a mixture of a single polymer andnon-polymeric materials, a combination of two or more polymericmaterials blended together, or a mixture of a blend of two or morepolymeric materials and non-polymeric materials.

As used herein, the term “copolymer” refers to polymers formed by thepolymerization reaction of at least two different monomers. For example,the term “copolymer” includes the co-polymerization reaction product ofethylene and an α-olefin, such as 1-hexene. The term “copolymer” is alsoinclusive of, for example, the co-polymerization of a mixture ofethylene, propylene, 1-butene, 1-hexene, and 1-octene. As used herein, acopolymer identified in terms of a plurality of monomers, e.g.,“propylene/ethylene copolymer”, refers to a copolymer in which eithermonomer may copolymerize in a higher weight or molar percent than theother monomer or monomers. However, the term “copolymer” as applied tofilm layers of the present invention refers to the first listed monomerpolymerized in a higher weight percent than the second listed monomer.

As used herein, terminology employing a “/” with respect to the chemicalidentity of a copolymer (e.g., polyvinylidene chloride/methyl acrylatecopolymer), identifies the comonomers which are copolymerized to producethe copolymer.

As used herein, the phrase “oxygen transmission rate” also known as“OTR” is measured according to ASTM D-3985-02 test method, a test knownto those skilled in the art. The oxygen transmission rate refers to thequantity of oxygen gas passing through a unit area of the parallelsurfaces of a film per unit time under the conditions of test, i.e.,cm³/100 in.²/24 h. or cm³/m²/24 h. The OTR of a film is measured afterthe film sample has equilibrated in a dry test environment and atstandard temperature and pressure conditions (STP) or at temperatureand/or pressure conditions as stated otherwise. Standard temperature andpressure conditions for measuring oxygen transmission rate are 32° F.(0° C.) and 1 atmosphere of pressure (0.1013 MPa). The “dry” environmentis considered to be one in which the relative humidity is less than 1%.

As used herein, the term “thermoformable” as applied to the presentinvention refers to films which are capable of being formed into adesired shape upon the application of heat, and are thermoformed aboutthe product on a support member by means of heat and differentialpressure. In the thermoforming process, virtually all of the air isevacuated from the interior of the package so that the film conformsvery closely to the contour of the packaged product.

As used herein, the phrase “unrestrained linear thermal shrinkage”, alsoknown as “linear free heat shrinkage”, refers to the irreversible andrapid reduction in linear dimension in a specified direction occurringin film subjected to elevated temperatures under conditions where nil ornegligible restraint to inhibit shrinkage is present. It is normallyexpressed as a percentage of the original dimension. As a result of themanufacturing process, internal stresses may be locked into the filmwhich can be released by heating. The temperature at which shrinkagewill occur is related to the processing techniques employed tomanufacture the film and may also be related to a phase transition inthe base resin. Thermoformable films according to the present inventionmay be characterized as having a low unrestrained linear thermalshrinkage, preferably, an unrestrained linear thermal shrinkage at 80°C. of less than 20%, more preferably, less than 10%, and mostpreferably, between 0-5% in both the machine and the transversedirections, as measured in accordance with ASTM D-2732-96 test method.

As used herein, the term “coextrusion” refers to the process ofextruding two or more materials through a single die with two or moreorifices arranged so that the extrudates merge and weld together into alaminar structure before chilling (chilling may also be termedquenching). The thermoformable films of the present invention may beformed using a coextrusion process, preferably, blown film coextrusion,cast film coextrusion, or extrusion coating, more preferably, blown filmcoextrusion, cast film coextrusion, and most preferably, blown filmcoextrusion.

As used herein, the term “polyester” refers to homopolymers orcopolymers having an ester linkage between monomer units which may beformed, for example, by condensation polymerization reactions between adicarboxylic acid and a glycol. The ester can be represented by thegeneral formula: [R—C(O)O—R′] where R and R′=alkyl group. Thedicarboxylic acid may be linear or aliphatic, i.e., oxalic acid, malonicacid, succinic acid, glutaric acid, adipic acid, pimelic acid, subericacid, azelaic acid, sebacic acid, and the like; or may be aromatic oralkyl substituted aromatic, i.e., various isomers of phthalic acid, suchas paraphthalic acid (or terephthalic acid), isophthalic acid andnaphthalic acid. Specific examples of alkyl substituted aromatic acidsinclude the various isomers of dimethylphthalic acid, such asdimethylisophthalic acid, dimethylorthophthalic acid,dimethylterephthalic acid, the various isomers of diethylphthalic acid,such as diethylisophthalic acid, diethylorthophthalic acid, the variousisomers of dimethylnaphthalic acid, such as 2,6-dimethylnaphthalic acidand 2,5-dimethylnaphthalic acid, and the various isomers ofdiethylnaphthalic acid. The glycols may be straight-chained or branched.Specific examples include ethylene glycol, propylene glycol,trimethylene glycol, 1,4-butane diol, neopentyl glycol and the like.Suitable materials of aromatic polyesters for use in the presentinvention include, but are not limited to, polyethylene terephthalate(PET), amorphous polyethylene terephthalate (APET), crystallinepolyethylene terephthalate (CPET), glycol-modified polyethyleneterephthalate (PETG), and polybutylene terephthalate; copolymers ofisophthalate, such as, polyethylene terephthalate/isophthalatecopolymer; and the like.

As used herein, the phrase “cycloaliphatic polyester” refers tocopolymers derived from a dicarboxylic acid component consisting of1,4-cyclohexanedicarboxylic, a diol component consists of1,4-cyclohexanedimethanol and polytetramethyleneether glycol.Cycloaliphatic polyesters are well known in the art and are described,for example, in U.S. Pat. Nos. 3,023,192; 3,261,812; 3,651,014;4,003,882; 4,221,703; and 4,349,469, all of which are incorporatedherein by reference.

As used herein, the phrase “polyolefin” refers to homopolymers,copolymers, including e.g. bipolymers, terpolymers, block copolymer,grafted copolymers, etc., having a methylene linkage between monomerunits which may be formed by any method known to those skill in the art.Examples of polyolefins include polyethylene (“PE”) which include, butare not limited to, low-density polyethylene “(LDPE”), linearlow-density polyethylene (“LLDPE”), very low-density polyethylene(“VLDPE”), ultra low-density polyethylene (“ULDPE”), medium-densitypolyethylene (“MDPE”), high-density polyethylene (“HDPE”), ultrahigh-density polyethylene (“UHDPE”), and polyethylenes comprisingethylene/α-olefin (“E/AO”) which are copolymers of ethylene with one ormore α-olefins (alpha-olefins) such as butene-1, hexene-1, octene-1, orthe like as a comonomer, and the like.

As used herein, the phrase “ethylene/α-olefin”, also known as “EAO”refers to a modified or unmodified copolymer produced by theco-polymerization of ethylene and any one or more α-olefin. The α-olefinin the present invention has between 3-20 pendant carbon atoms,preferably, 3-12 pendant carbon atoms and more preferably, 3-6 pendantcarbon atoms. The co-polymerization of ethylene and an α-olefin may beproduced by heterogeneous catalysis, i.e., co-polymerization reactionswith Ziegler-Natta catalysis systems, for example, metal halidesactivated by an organometallic catalyst, i.e., titanium chloride,optionally containing magnesium chloride, complexed to trialkyl aluminumand maybe found in patents such as U.S. Pat. No. 4,302,565 to Goeke, etal. and U.S. Pat. No. 4,302,566 to Karol, et al., both of which arehereby incorporated, in their entireties, by reference thereto.Heterogeneous catalyzed copolymers of ethylene and an α-olefin mayinclude linear low density polyethylene, very low density polyethyleneand ultra low density polyethylene. These copolymers of this type areavailable from, for example, The Dow Chemical Company, of Midland,Mich., U.S.A. and sold under the trademark DOWLEX™ resins. Additionally,the co-polymerization of ethylene and a α-olefin may also be produced byhomogeneous catalysis, for example, co-polymerization reactions withmetallocene catalysis systems which include constrained geometrycatalysts, i.e., monocyclopentadienyl transition-metal complexes taughtin U.S. Pat. No. 5,026,798, to Canich, the teachings of which areincorporated herein by reference. Homogeneous catalyzedethylene/α-olefin copolymers may include ethylene/α-olefin copolymersavailable from The Dow Chemical Company, known as AFFINITY™ and ATTANE™resins, TAFMER™ linear copolymers obtainable from the MitsuiPetrochemical Corporation of Tokyo, Japan and ethylene/α-olefincopolymers known as EXACT™ resins obtainable from ExxonMobil ChemicalCompany of Houston, Tex., U.S.A.

As used herein, the terms “heat-seal”, “heat-sealing”, “heat-sealable”,and the like refer to a first portion of a film surface (i.e., formedfrom a single layer or multiple layers) which is capable of forming afusion bond to a second portion of a film surface. A heat-seal layer iscapable of fusion bonding by conventional indirect heating means whichgenerate sufficient heat on at least one film contact surface forconduction to the contiguous film contact surface and formation of abond interface therebetween without loss of the film integrity. Itshould be recognized that heat sealing can be performed by any one ormore of a wide variety of manners, such as using a heat seal technique(e.g., melt-bead sealing, thermal sealing, impulse sealing, ultrasonicsealing, hot air, hot wire, infrared radiation, etc.) and most ofteninvolves application of heat and pressure for a time sufficient tocreate a seal upon cooling.

As used herein, the phrase “innermost exterior-film layer” as applied tofilm layers of the present invention refers to the exterior-film layerwhich is closest to the product relative to the other layers of themultilayer film. The phrase “exterior-film layer” as applied to filmlayers refers to any film layer having less than two of its principalsurfaces directly adhered to another layer of the substrate or anothersubstrate. In contrast, the phrase “outermost exterior-film layer”, asused herein refers to the exterior-film layer which is furthest from theproduct relative to the other layers of the multilayer film.

As used herein, the phrase “interior-film layer” as applied to filmlayers refers to any film layers having both of its principal surfacesdirectly adhered to another layer of the film.

As used herein, the phrase “gloss” refers to the specular gloss of thefilms of the present invention, which is a measure of the relativeluminous reflectance factor of a specimen in the mirror direction. Therelative luminous reflectance factor is the amount of light reflected bythe surface of the specimen in reference to a standard and the angle ofreflection (20°, 45°, 60° or 85°). Gloss as it refers to the presentinvention, means that property of a film measured according to ASTMD-2457-03 test method. The specular gloss of the films of the presentinvention are determined by using BYK Gardner micro TRI Glossmeter.

As used herein, the phrase “haze” refers to that percentage oftransmitted light which in passing through the film specimen deviatesfrom the incident beam by forward scattering, and which is measured inaccordance with ASTM D-1003-00 test method, a test known to thoseskilled in the art.

As used herein, the phrase “tie layer” refer to any film layer whichfunctions toadhere two layers to one another. The tie layer may compriseany polymer, copolymer or blend of polymers having a polar groupthereon, or any other polymer, copolymer or blend of polymers whichprovide sufficient interlayer adhesion to adjacent layers comprisingotherwise nonadhering polymers. Suitable materials for use as tie layersin the present invention may include, but are not limited to, ionomers,ethylene/vinyl acetate copolymers (E/VA), anhydride-modifiedethylene/vinyl acetate copolymers (“m-E/VA”), ethylene/methacrylic acidcopolymers (“E/MAA”), ethylene/methyl acrylate copolymers (E/MA),ethylene/ethyl acrylate copolymers (E/EA), anhydride-modifiedethylene/α-olefin copolymers (“m-E/AO”), anhydride-modified polyolefins,such as anhydride-modified polyethylene (“m-PE”), or a blend thereof.

As used herein, the term “anhydride-modified” refers to any form ofanhydride functionality, such as the anhydride of maleic acid, fumaricacid, etc., whether co-polymerized with an anhydride-containing monomerwith a second, different monomer, grafted onto a polymer or copolymer,or blended with one or more polymers, and is inclusive of derivatives ofsuch functionalities, such as acids, esters, and metal salts derivedtherefrom.

As used herein, the phrase “bulk layer” refers to any film layer whichserves to increase the abuse resistance, toughness, and modulus of amultilayer film.

As used herein, the phrase “thermoforming-assist layer” refers to anyinterior-film layer which functions to increase the integrity of themultilayer film while the film is heated and drawn into a cavity duringthe thermoforming process.

As used herein, the phrase “machine direction” refers to a direction“along the length” of the film, i.e., in the elongate direction of thefilm as the film is formed during extrusion, lamination, and/or coating.

As used herein, the phrase “transverse direction” refers to a directionacross the film, perpendicular to the machine or longitudinal direction.

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete and will fully conveythe scope of the invention to those skilled in the art.

Referring to FIG. 1, film 10 is a schematic, cross-sectional view of oneembodiment of a multilayered film according to the present inventioncomprising a first polymeric layer 11, a second polymeric layer 12, athird polymeric layer 13, and a fourth polymeric layer 14. Film 10 hasfour layers: two exterior-film layers (11, 14); and two interior-filmlayers (12, 13). As depicted, polymeric first layer 11 is an innermostexterior-film layer which may comprise either a cycloaliphatic polyesteror an aromatic polyester, such as, for example, polyethyleneterephthalate (PET). Layer 12 is an interior-film tie layer and maycomprise any adhesive material which serves to adhere layer 11 and 13 toitself. Preferably, layer 12 comprises an adhesive material derived fromcopolymers of ethylene and an alkyl acrylate, i.e., for example,ethylene/methacrylate copolymers (E/MA). Layer 13 serves as athermoforming-assist layer and may comprise any polyolefin, preferably,either a homopolymer or copolymer of polypropylene (PP) or a homopolymeror a copolymer of a cross-linked polyethylene (PE). Layer 14 is aninnermost exterior-film layer which includes a heat-sealing material,preferably, a heat-sealing polyolefin. Suitable heat-sealablepolyolefins for use in layer 14 may include, not are not limited to, forexample, polyethylene (PE), which includes ultra low-densitypolyethylene (ULDPE), linear low-density polyethylene (LLDPE),low-density polyethylene (LDPE), medium-density polyethylene (MDPE),polypropylene (PP), ethylene/vinyl acetate (E/VA), copolymers ofethylene or propylene with one or more α-olefins, and ionomers. Otherexamples of suitable heat-sealable polyolefins include cyclic olefincopolymers (COC), ethylene/propylene copolymers (PE/P), polypropylene(PP), propylene/ethylene copolymer (PP/E), polyisoprene, polybutylene(PB), polybutene-1, poly-3-methylbutene-1, and copolymers of ethyleneand 4-methylpentene-1, and the like.

It will be appreciated that films according to the present invention arenot limited to the four-layered structure, i.e., layers 11, 12, 13, and14, provided that layers 11 and 14 are positioned as exterior-filmlayers and layer 13 is an interior-film layer which functions as athermoforming-assist layer. Layer 13 may be placed in any positionwithin the film structure and, preferably, is in direct contact withlayer 11, by either a fusion bond to layer 11 or through contact withtie layer 12. It is within the scope of the present invention thatadditional interior layers may be included in the film structureprovided that the oxygen transmitability of the entire structure doesnot decrease below 2 cm³/100 in²/24 h. (31 cm³/m²/24 h.) as measured inaccordance with ASTM D-3985-02. Thus, the film of this invention mayinclude any number of additional layers in any position between eitheroutermost exterior-film layer 11 and innermost exterior-film layer 14 orbetween interior-film layer 13 and innermost exterior-film layer 14. Itis contemplated that the films of the present invention may comprise atleast three layers, and may include a total of four layers, five layers,seven layers, or any number of layers so desired.

Turning now to FIG. 2, film 20 is schematic, cross-sectional view of oneembodiment of a multilayered film according to the present inventioncomprising a seven-layer film structure. Film 20 includes a firstpolymeric layer 21, a second polymeric layer 22, a third polymeric layer23, a fourth polymeric layer 24, a fifth polymeric layer 25, a sixthpolymeric layer 26, and a seventh polymeric layer 27, in which thereexists two exterior-film layers (21, 27), and five interior-film layers(22, 23, 24, 25, 26). Layers 21, 22 and 23 may each have identicalcompositions and sub-structure as described for layers 11, 12 and 13,respectively, of film 10, as described hereinabove. As depicted, layer21 is an outermost exterior-film layer and layers 22 and 23 being bothinterior-film layers which serve as a tie layer and thermoforming-assistlayer, respectively. Layers 24 and layer 25 function as bulk layers andmay both be formed from the same material or different materials.Preferably, layers 24 and 25 comprise any thermoplastic material, morepreferably, any polyolefin resin, and most preferably, homopolymers andcopolymers of polyethylene (PE), polypropylene (PP), polybutylene (PB)or blends thereof. Layer 26 is an interior-film layer which may serve aseither a bulk layer or a tie layer. As a bulk layer, layer 26 preferablycomprises any thermoplastic material, more preferably, any polyolefinresin, and most preferably, homopolymers and copolymers of polyethylene(PE), polypropylene (PP), polybutylene (PB) or blends thereof. As a tielayer, layer 26 preferably comprises any adhesive material which bondslayers 25 and 27 to itself. Suitable polyolefins include, but are notlimited to, for example, homopolymers and copolymers of polyethylene(PE), polypropylene (PP), polybutylene (PB) or blends thereof. It ispreferred that the modified polyolefin comprise anhydride-modifiedpolyolefin, which, but are not limited to, ionomers, ethylene/vinylacetate copolymers (E/VA), anhydride-modified ethylene/vinyl acetatecopolymers (m-E/VA), ethylene/methacrylic acid copolymers (E/EAA),ethylene/methyl acrylate copolymers (E/MA), ethylene/ethyl acrylatecopolymers (E/EA), anhydride-modified ethylene/α-olefin copolymers(m-E/AO), anhydride-modified polyolefins, such as anhydride-modifiedpolyethylene (m-PE), or a blend thereof.

It will also be recognized by those skilled in the art that films 10, 20and any variations thereof may be used to form flexible, semi-rigid andrigid containers, packages, pouches or any portion thereof. In generalthe films and packages of the present invention can be used in thepackaging of any product, the films and packages of the presentinvention are especially advantageous for the packaging of foodproducts, especially fresh meat products. Among the fresh meat productwhich can be packaged in the films and packages according to the presentinvention are poultry, pork, beef, lamb, goat, horse, and fish.

It will be appreciated that the thicknesses of each of films 10, 20 andany variations thereof may vary and equal thicknesses in the FIGS. 1 and2 are presented only to facilitate illustration.

It will also be appreciated that the films of the present invention havean oxygen transmission rate at 73° C. and 0% R.H. of preferably between2-1000 cm³/100 in²/24 h. (31-15,500 cm³/m²/24 h.), more preferably,between 10-1000 cm³/100 in²/24 h. (155-15,500 cm³/m²/24 h.), and mostpreferably, between 20-1000 cm³/100 in²/24 h. (310-15,500 cm³/m²/24 h.)as measured in accordance with ASTM D-3985-02 test method.

The films of the present invention may be formed by any conventionaltechnique for forming films, including extrusion lamination, castextrusion, extrusion coating, and coextrusion, preferably, extrusioncoating, cast coextrusion or blown film coextrusion, and morepreferably, cast coextrusion or blown film coextrusion, most preferably,blown coextrusion. In blown coextrusion, for example, the films of thepresent invention may be produced by a single-bubble blown film process.In this process a tubular film is produced using one or more extruders(the number of extruders depends upon the number of layers in the filmand each layer composition). The polymer resins extruded by theextruders are fed to a circular die head through which the film layersare forced and formed into a cylindrical multilayer film bubble. Thebubble is extruded therefrom through an air ring and quenched e.g., viacooled water bath, solid surface and/or air, and then ultimatelycollapsed and formed into a multilayer film.

In the practice of this invention, it may be desirable to have one ormore layers of the entire film cross-linked to improve thethermoformability, abuse and/or puncture resistance and/or otherphysical characteristics of the entire film. Crosslinking is thepredominant reaction which results in the formation of carbon-carbonbonds between polymer chains. Crosslinking may be accomplished, forexample, by ionized radiation means such as high energy electrons,gamma-rays, beta particles and the like, or through chemical means byuse of peroxides and the like. More particularly, for crosslinking withionizing radiation, the energy source can be any electron beam generatoroperating in a range of about 150 kilovolts to about 6 megavolts with apower output capable of supplying the desired dosage. The voltage can beadjusted to appropriate levels which may be for example 1 to 6 millionvolts or higher or lower. Many apparatus for irradiating films are knownto those skilled in the art. The films of the present invention may beirradiated at a level of from 2-12 MRads, more preferably 2-5 MRads. Themost preferred amount of radiation is dependent upon the film and itsend use.

One method for determining the degree of “cross-linking” or the amountof radiation absorbed by a material is to measure the gel content inaccordance with ASTM D-2765-01 which is hereby incorporated, in itsentirety, by reference. Gel content corresponds to the relative extentof crosslinking within a polymeric material having undergoneirradiation.

Preferably, the coextruded multilayered packaging film of the presentinvention can have any total film thickness desired, preferablythicknesses may range between 0.8-15 mils (20.32-381 μm), morepreferably, between 0.8-10 mils (20.32-254 μm), and most preferably,between 0.8-8.0 mil (20.32-203.2 μm).

EXAMPLES

The invention is illustrated by the following examples, which areprovided for the purpose of representation, and are not to be construedas limiting the scope of the invention.

Unless otherwise noted, the thermoplastic resins utilized in the presentinvention are generally commercially available in pellet form and, asgenerally recognized in the art, may be melt blended or mechanicallymixed by well-known methods using commercially available equipmentincluding tumblers, mixers or blenders. Also, if desired, well knownadditives such as processing aids, slip agents, anti-blocking agents andpigments, and mixtures thereof may be incorporated into the film, byblending prior to extrusion. The resins and any additives are introducedto an extruder where the resins are melt plastified by heating and thentransferred to an extrusion (or coextrusion) die for formation into atube. Extruder and die temperatures will generally depend upon theparticular resin or resin containing mixtures being processed andsuitable temperature ranges for commercially available resins aregenerally known in the art, or are provided in technical bulletins madeavailable by resin manufacturers. Processing temperatures may varydepending upon other processing parameters chosen.

For the following examples, a single slash, “/”, represents the divisionbetween individual layers within a film structure.

Example 1

Example 1 is one embodiment of the present invention of a film havingseven layers (see film 20 in FIG. 2). The first polymeric layer (21)comprised a mixture of polyester, anti-block additive and slip additive.The polyester comprised polyethylene terephthalate copolymer having adensity of 1.4 g/cm³, a melting point of 240° C., a tensile strength atbreak (machine direction/transverse direction) of 8.4/5.6 kpsi, and isavailable under the trademark Voridian™ Polymer 9921 from EastmanChemical Company, Kingsport, Tenn., U.S.A. In Example 1, the secondlayer (22) was a tie layer comprising ethylene/methyl acrylate copolymer(E/MA) and modified linear low-density polyethylene (m-LLDPE). Theethylene/methyl acrylate copolymer has a density of 0.948 g/cm³, amelting point of 49° C., a melt index of 2.0 g/10 min., and is availablefrom Eastman Chemical Company, Kingsport, Tenn., U.S.A. The modifiedlinear low-density polyethylene was an anhydride linear low-densitypolyethylene having a having a density of 0.92 g/cm³, a melting point of125° C., a melt index of 1.5 g/10 min., a Vicat softening point of 102°C., and is available under the trademark Bynel® from E. I. du Pont deNemours and Company, Wilmington, Del., U.S.A. The third layer (23) andthe sixth layer (26) each comprised a polypropylene random copolymer(PP) having a melt index of 2 g/10 min., a tensile strength at break of4.5 kpsi, and is sold as Grade 8244 from BP Amoco Polymers, Inc.,Naperville, Ill., U.S.A. The fourth layer (24) and the fifth layer (25)each comprised an ultra low-density polyethylene (ULDPE), particularly,an ethylene/octene α-olefin copolymer (E/AO) having a density of 0.912g/cm³, a melting point of 123° C., a melt index of 1.0 g/10 min., aVicat softening point of 93° C., a is available under the trademarkAttane 4201G from The Dow Chemical Company, Midland, Mich., U.S.A. Theseventh layer (27) comprised polyethylene (PE) and anti-block additive.The polyethylene was identical to that used in the fourth and fifthlayers of the film. The Example 1 was produced having an overall filmthickness of about 5 mil and with the following structure and relativelayer thicknesses, beginning with the outermost exterior-film layer andgoing to the innermost exterior-film layer (left to right):

5% PET/15% E/MA/10% PP/12% PE/8% PE/27% PP/23% PE

Example 1 had an oxygen transmission rate at 73° C. and 0% R.H. of 40cm³/100 in²/24 h. (620 cm³/m²/24 h.) as measured in accordance with ASTMD-3985-02 test method. Example 2

In Example 2, the film is another example of a seven-layer embodiment ofthe present invention. All the film layers are identical in structureand relative layer thickness as that used in Example 1, except that theoverall film thickness was about 8 mil.

Example 2 had an oxygen transmission rate at 73° C. and 0% R.H. of 20cm³/100 in²/24 h. (310 cm³/m²/24 h.) as measured in accordance with ASTMD-3985-02 test method.

Unless otherwise noted, the physical properties and performancecharacteristics reported herein were measured by test procedures similarto the following methods. The following ASTM test procedures are eachincorporated herein by reference in their entireties. Density ASTMD-1505 Gel Content ASTM D-2765-01 Gloss ASTM D-2457-03 Haze ASTMD-1003-00 Unrestrained Linear Thermal Shrinkage ASTM D-2732-96 MeltIndex ASTM D-1238 Melting Point ASTM D-3417 Oxygen Transmission RateASTM D-3985-02 Tensile Strength at Break ASTM D-882 Vicat SofteningTemperature ASTM D-1525

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. Therefore, it is to be understood that theinvention is not to be limited to the specific embodiments disclosed andthat modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

1. A thermoformable coextruded packaging film comprising: (a) at least afirst polymeric layer, a second polymeric layer, and a third polymericlayer; (b) wherein said first polymeric layer is an outermostexterior-film layer and comprises a material selected from the groupconsisting of cycloaliphatic polyesters, polyethylene terephthalate(PET), polyethylene terephthalate glycol (PETG), polypropyleneterephthalate (PPT), polybutylene terephthalate (PBT) and blendsthereof.; (c) wherein said second polymeric layer comprisespolypropylene or cross-linked polyethylene; (d) wherein said thirdpolymeric layer is an innermost exterior-film layer comprising aheat-sealable polyolefin; (e) wherein said film has an oxygentransmission rate at 73° C. and 0% R.H. of between 2-1000 cm³/100 in²/24h. (31-15,500 cm³/m²/24 h.) as measured in accordance with ASTMD-3985-02 test method; and (f) wherein said film comprises anunrestrained linear thermal shrinkage at 80° C. of 0-20% in both themachine and transverse direction as measured in accordance with ASTMD-2732-96 test method.
 2. A thermoformable coextruded packaging filmaccording to claim 1, wherein said film is formed by blown filmcoextrusion.
 3. A thermoformable coextruded packaging film according toclaim 1, wherein said first polymeric layer, said second polymericlayer, and said third polymeric layer are free of polyamide.
 4. Athermoformable coextruded packaging film according to claim 1, whereinsaid film comprises an unrestrained linear thermal shrinkage at 80° C.of 0-10% in both the machine and transverse direction as measured inaccordance with ASTM D-2732-96 test method.
 5. A thermoformablecoextruded packaging film according to claim 4, wherein said filmcomprises an unrestrained linear thermal shrinkage at 80° C. of 0-5% inboth the machine and transverse direction as measured in accordance withASTM D-2732-96 test method.
 6. A thermoformable coextruded packagingfilm according to claim 1, wherein said film comprises a gloss value at45° of at least 60% as measured in accordance ASTM D-2457-03 testmethod.
 7. A thermoformable coextruded packaging film according to claim1, wherein said film comprises a haze value of less than 20% as measuredin accordance with ASTM D-1003-00 test method.
 8. A thermoformablecoextruded packaging film according to claim 1, wherein said film has anoxygen transmission rate at 73° C. and 0% R.H. of between 10-1000cm³/100 in²/24 h. (155-15,500 cm³/m²/24 h.) as measured in accordancewith ASTM D-3985-02 test method.
 9. A thermoformable coextrudedpackaging film according to claim 1, wherein said film has an oxygentransmission rate at 73° C. and 0% R.H. of between 20-1000 cm³/100in²/24 h. (310-15,500 cm³/m²/24 h.) as measured in accordance with ASTMD-3985-02 test method.
 10. A thermoformable coextruded packaging filmaccording to claim 1, wherein said third polymeric layer comprisespolyethylene.
 11. A thermoformable multilayer packaging film accordingto claim 1, wherein said film further comprises a fourth polymeric layerdisposed between said first and second polymeric layers.
 12. Athermoformable coextruded packaging film according to claim 11, whereinsaid film further comprises a fifth polymeric layer disposed betweensaid second and third polymeric layers.
 13. A thermoformable coextrudedpackaging film according to claim 11, wherein said fourth polymericlayer comprises a polyalkyl acrylate copolymer or blend thereof.
 14. Athermoformable coextruded packaging film according to claim 13, whereinsaid polyalkyl acrylate copolymer comprises an ethylene/alkyl acrylatecopolymer or blends thereof.
 15. A thermoformable coextruded packagingfilm according to claim 14, wherein said ethylene/alkyl acrylatecopolymers comprise a material selected from the group consisting ofethylene/methyl acrylate copolymer (E/MA), ethylene/ethyl acrylatecopolymer (E/EA), ethylene/butyl acrylate copolymer (E/BA), andethylene/methyl methacrylate copolymer (E/MMA).
 16. A thermoformablecoextruded packaging film according to claim 12, wherein said fifthpolymeric layer comprises a material selected from the group consistingof polypropylene, polyethylene, anhydride-modified polyolefin and blendsthereof.
 17. A thermoformable coextruded packaging film according toclaim 12, wherein said film further comprises a sixth polymeric layerand a seventh polymeric layer.
 18. A thermoformable coextruded packagingfilm according to claim 17, wherein said sixth and seventh polymericlayers each comprises a material selected from the group consisting ofpolyethylene, polypropylene and blends thereof.
 19. A thermoformablecoextruded packaging film according to claim 1, wherein said film has athickness range between 0.8-15 mils (20.32-381 μm).
 20. A thermoformablecoextruded packaging film according to claim 19, wherein said film has athickness range between 0.8-10 mils (20.32-254 μm).
 21. A thermoformablecoextruded packaging film according to claim 20, wherein said film has athickness range between 0.8-8.0 mil (20.32-203.2 μm).
 22. Athermoformable coextruded packaging film according to claim 1, whereinsaid film forms a package or a portions thereof.
 23. A thermoformablecoextruded packaging film comprising: (a) at least a first polymericlayer, a second polymeric layer, a third polymeric layer, a fourthpolymeric layer, and a fifth polymeric layer; (b) wherein said firstpolymeric layer is an outermost exterior-film layer and comprises amaterial selected from the group consisting of cycloaliphaticpolyesters, polyethylene terephthalate (PET), polyethylene terephthalateglycol (PETG), polypropylene terephthalate (PPT), polybutyleneterephthalate (PBT) and blends thereof.; (c) wherein said secondpolymeric layer is directly contacting said first and third polymericlayers and comprises an polyalkyl acrylate copolymer or blend thereof;(d) wherein said third polymeric layer is directly contacting saidsecond and fourth polymeric layers and comprises either polypropylene orcross-linked polyethylene; (e) wherein said fourth polymeric layer isdirectly contacting said third and fifth polymeric layers and comprisesa material selected from the group consisting of polyethylene,polypropylene, anhydride-modified polyolefin and blends thereof; (f)wherein said fifth polymeric layer is directly contacting said fourthand sixth polymeric layers and comprises a heat-sealable polyolefin; (g)wherein said film has an oxygen transmission rate at 73° C. and 0% R.H.of between 2-1000 cm³/100 in²/24 h. (31-15,500 cm³/m²/24 h.) as measuredin accordance with ASTM D-3985-02 test method; and (h) wherein said filmcomprises an unrestrained linear thermal shrinkage at 80° C. of 0-5% inboth the machine and transverse direction as measured in accordance withASTM D-2732-96 test method.
 24. A thermoformable coextruded packagingfilm according to claim 23, wherein said film is formed by blown filmcoextrusion.
 25. A thermoformable coextruded packaging film comprising:(a) at least a first polymeric layer, a second polymeric layer, a thirdpolymeric layer, a fourth polymeric layer, a fifth polymeric layer, asixth polymeric layer, and a seventh polymeric layer; (b) wherein saidfirst polymeric layer is an outermost exterior-film layer and comprisesa material selected from the group consisting of cycloaliphaticpolyesters, polyethylene terephthalate (PET), polyethylene terephthalateglycol (PETG), polypropylene terephthalate (PPT), polybutyleneterephthalate (PBT) and blends thereof.; (c) wherein said secondpolymeric layer is directly contacting said first and third polymericlayers and comprises an polyalkyl acrylate copolymer of blend thereof;(d) wherein said third polymeric layer is directly contacting saidsecond and fourth polymeric layers and comprises either polypropylene orcross-linked polyethylene; (e) wherein said fourth polymeric layer isdirectly contacting said third and fifth polymeric layers and comprisesa material selected from the group consisting of polyethylene,polypropylene and blends thereof; (f) wherein said fifth polymeric layeris directly contacting said fourth and sixth polymeric layers andcomprises a material selected from the group consisting of polyethylene,polypropylene and blends thereof; (g) wherein said sixth polymeric layeris directly contacting said fifth and seventh polymeric layers andcomprises a material selected from the group consisting of polyethylene,polypropylene, anhydride-modified polyolefin and blends thereof; (h)wherein said seventh polymeric layer is an innermost exterior-film layercomprising a heat-sealable polyolefin; (i) wherein said film has anoxygen transmission rate at 73° C. and 0% R.H. of between 2-1000 cm³/100in²/24 h. (31-15,500 cm³/m²/24 h.) as measured in with ASTM D-3985-02test method; and (j) wherein said film comprises an unrestrained linearthermal shrinkage at 80° C. of 0-5% in both the machine and transversedirection as measured in accordance with ASTM D-2732-96 test method. 26.A thermoformable coextruded packaging film according to claim 25,wherein said film is formed by blown film coextrusion.
 27. Athermoformable coextruded packaging film according to claim 25, whereinsaid first polymeric layer, said second polymeric layer, said thirdpolymeric layer, said fourth polymeric layer, said fifth polymericlayer, said sixth polymeric layer, and said seventh polymeric layer arefree of polyamide.
 28. A thermoformable coextruded packaging filmaccording to claim 25, wherein said film comprises a gloss value at 45°of at least 60% as measured in accordance ASTM D-2457 test method.
 29. Athermoformable coextruded packaging film according to claim 25, whereinsaid film comprises a haze value of less than 20% as measured inaccordance with ASTM D-1003-00 test method.
 30. A thermoformablecoextruded packaging film according to claim 25, wherein said film hasan oxygen transmission rate at 73° C. and 0% R.H. of between 10-1000cm³/100 in²/24 h. (155-15,500 cm³/m²/24 h.) as measured in accordancewith ASTM D-3985-02 test method.
 31. A thermoformable coextrudedpackaging film according to claim 30, wherein said film has an oxygentransmission rate at 73° C. and 0% R.H. of between 20-1000 cm³/100in²/24 h. (310-15,500 cm³/m²/24 h.) as measured in accordance with ASTMD-3985-02 test method.
 32. A thermoformable coextruded packaging filmaccording to claim 25, wherein said fourth polymeric layer comprises apolyalkyl acrylate copolymer or blend thereof.
 33. A thermoformablecoextruded packaging film according to claim 32, wherein said polyalkylacrylate copolymer comprises an ethylene/alkyl acrylate copolymers orblends thereof.
 34. A thermoformable coextruded packaging film accordingto claim 33, wherein said ethylene/alkyl acrylate copolymers comprise amaterial selected from the group consisting of ethylene/methyl acrylatecopolymer (E/MA), ethylene/ethyl acrylate copolymer (E/EA),ethylene/butyl acrylate copolymer (E/BA), and ethylene/methylmethacrylate copolymer (E/MMA).
 35. A thermoformable coextrudedpackaging film according to claim 25, wherein said anhydride-modifiedpolyolefin comprise an anhydride modified-polyethylene.
 36. Athermoformable coextruded packaging film according to claim 25, whereinsaid heat-sealable polyolefin comprises polyethylene.
 37. Athermoformable coextruded packaging film according to claim 25, whereinsaid film has a thickness range between 0.8-15 mils (20.32-381 μm). 38.A thermoformable coextruded packaging film according to claim 37,wherein said film has a thickness range between 0.8-10 mils (20.32-254μm).
 39. A thermoformable coextruded packaging film according to claim38, wherein said film has a thickness range between 0.8-8.0 mil(20.32-203.2 μm).
 40. A thermoformable coextruded packaging filmaccording to claim 25, wherein said film forms a package or a portionthereof.